In conventional switching circuits, the potential of a back gate of a power MOSFET is set to the potential of a source. For this reason, the back gate and the source of the power MOSFET is short-circuited. In other words, a parasitic diode between the back gate and the source of the power MOSFET is short-circuited. Therefore, if a power supply is reversely connected, a large current can flow to a load via the parasitic diode between the back gate and a drain of the power MOSFET.